For example, according to US 2005/0074343 A1 (JP-A-2005-110478), a fuel pump includes a brushless motor. In general, a motor (brush-type motor) having contact brushes causes losses such as slide resistance between a commutator and a brush, electric resistance between the commutator and the brush, and fluid resistance caused by grooves, via which the commutator is divided into segments. By contrast, a brushless motor may not cause the above losses arising in the brush-type motor. Therefore, a brushless motor is higher than a brush-type motor in motor efficiency, so that a fuel pump having a brushless motor is enhanced in pump efficiency. Here, the pump efficiency is a ratio of an amount of work produced by the fuel pump relative to electricity supplied to the fuel pump. The amount of work produced by the fuel pump can be calculated by multiplying fuel discharge pressure by a fuel discharge amount.
When the amount of work is constant, as the efficiency of the fuel pump increases, a motor portion can be downsized, so that the fuel pump can be downsized. A fuel pump including a brushless motor may be applied to a small vehicle such as a motor cycle.
A fuel pump including a brush-type motor has a stator core that is located radially outside a rotator. The outer circumferential periphery of the stator core is surrounded by a housing for restricting fuel from leaking. The housing is not necessary to form a magnetic circuit in a brushless motor. According to US 2005/0074343 A1, the thickness of the housing is larger in a portion surrounding the outer circumferential periphery of the stator core. Accordingly, in this structure, the outer diameter of the housing surrounding the stator core is relatively large. Consequently, it is difficult to reduce the outer diameter of the fuel pump.